Joined: Dec 8, 2007
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ends with an 's'. English grammatical rules state that words that end with an 's' don't get ''s' after them, just the ' (Petrus' not Petrus's). Besides it just looks better that way.
"Put more stuff in the... thing where... more stuff goes in."
Joined: Mar 21, 2008
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English orthographical rules state an apostrophe is put after the plural -s (dog's vs. dogs'). American spelling often puts it after all s's, but "Petrus's" is still a valid option.
Joined: Dec 2, 2007
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No. It's "Petrus's". Just the ' is a common misconception. The only place you use just an ' is for plural words ending in S and for "Jesus" and "Moses".
Joined: Dec 8, 2007
Occupation: Junior Scientist
Location: Not California
Interests: Physics and Astronomy, Exoplanets, Singing praise to Valpurus while smashing skulls with a bloody warhammer, Jogging
Posts: 2,920
It looks better.
"Put more stuff in the... thing where... more stuff goes in."
Joined: Dec 2, 2007
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Location: Under a pile of my own offspring
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Either is correct, Petrus' or Petrus's. Did you know that the 's is not added to words that end in z because it makes it difficult to pronounce. Eg Gomez' head exploded as the bullet ripped through it.